1. Field of the Invention
The present invention relates to an epoxy resin composition for encapsulating a semiconductor and a semiconductor device using the same.
2. Description of the Related Art
In an electronic device such as a diode, a transistor or an IC (Integrated Circuit), an epoxy resin composition is conventionally used for encapsulating. Particularly, an epoxy resin composition comprising an epoxy resin, a phenolic resin and an inorganic filler such as fused silica or crystalline silica and excellent in heat resistance and moisture resistance is used for the IC. Recently, however, a market trend is inclined to downsizing, weight saving and high-end product of electronics, and thereby a highly integrated semiconductor device is continuously under development. Additionally, a surface mount type semiconductor device is becoming popular more and more. In the circumstances, a demand for the epoxy resin composition for encapsulating a semiconductor element is increasing severe. Particularly, in the circumstance that a surface mount type semiconductor device is becoming general, the semiconductor device which absorbed moisture is subjected to a high temperature environment during a solder reflow treatment. Furthermore, as a part of a zero-emission movement, replacement to a lead-free solder is proceeded. Such a lead-free solder has a higher melting point than that of the conventional solder, and thereby requires a reflow temperature of 260° C., which is 20° C. higher than that of the conventional solder, when mounting on a surface. Thereby, the semiconductor device is subjected to a higher temperature environment than ever, which is apt to cause a defect greatly detracting the reliability of the semiconductor device such as delamination at an interface between a semiconductor element or a lead frame and a cured product of the epoxy resin composition, or a crack in the semiconductor device.
Also, with regard to the lead frame, from the viewpoint of excluding any lead, the number of a semiconductor device in which a preplating frame plated with Ni, Ni—Pd, Ni—Pd—Au or the like in advance is used instead of solder plating on outer lead is increasing. However, such plating has a problem of notably poor adhesion with a cured product of the epoxy resin composition, which may cause delamination at the interface when mounting on a surface. Therefore, there is a demand for preventing such a defect, that is, a demand for an improvement in solder reflow resistance.
On the other hand, from the environmental concerns, there is a movement for restricting a use of a halogen based flame retardant such as a bromine-contained organic compound or the like, and an antimony compound such as diantimony trioxide, diantimony tetraoxide or the like, which are conventionally used as a flame retardant in a encapsulant for the semiconductor. Therefore, there is a demand for a new flame retardant technology for replacing the conventional one. As such a replacing flame retardant technology in a encapsulant for semiconductor, there is proposed a method using a metal hydroxide such as aluminum hydroxide, magnesium hydroxide or the like, which is less harmful to the environment. However, this method has a problem that a large amount of the metal hydroxide is required to obtain an expected flame retardant effect. Additionally, if the compound ratio of the metal hydroxide is increased to obtain a sufficient flame resistance, the flowability and curability of the epoxy resin composition during molding are decreased, and the mechanical strength of the cured product is deteriorated. As a result, the solder reflow resistance is deteriorated in the temperature range of mounting the lead-free solder.
In order to prevent the deterioration of the solder reflow resistance associated with the increase of the mounting temperature, an epoxy resin or a curing agent having a low water absorption rate respectively is used (e.g. Japanese Patent Application Laid-open Nos. Hei 1-275618 (pp. 1 to 5) and Hei 5-097965 (pp. 2 to 6) and Hei 5-097967 (pp. 2 to 7)). However, such an epoxy resin composition does not have a sufficient flame resistance and thereby requires addition of a flame retardant. Additionally, such an epoxy resin composition exhibits a low adhesion to the preplating frame. Thereby, the reliability is low, particularly in a package using such a preplating frame.
Furthermore, such an epoxy resin composition has a low crosslinking density and thereby a molded article immediately after curing is so soft that a problem may arise in a continuous molding process such as an insufficient release of the resin from the mold, which may reduce productivity.
In order to improve productivity, there is proposed a method adding oxidized polyethylene (e.g. Japanese Patent Application Laid-open Nos. Hei 8-258077 (pp. 2 to 9) and Hei 11-152393 (pp. 2 to 5)). However, it is required to increase a compounding amount of oxidized polyethylene in order to obtain sufficient releasing property owing to oxidized polyethylene only. In this case, the adhesion is deteriorated. Furthermore, in order to improve the dispersibility of oxidized polyethylene, there is proposed a method using epoxy polyether silicone having dimethyl siloxane structure as a main chain together (e.g. Japanese Patent Application Laid-open No. Hei 5-315472 (pp. 2 to 7)). Although a silicone oil having a polyether chain greatly contributes to improvement of productivity, the solder reflow resistance is deteriorated because of increased moisture absorption due to the polyether chain.
In order to improve the solder reflow resistance, there is also proposed a method using a resin having flexibility and flame resistance in addition to a low water absorption property (e.g. Japanese Patent Application Laid-open Nos. Hei 1-275618 (pp. 1 to 5), Hei 5-097965 (pp. 2 to 6) and Hei 5-097967 (pp. 2 to 7)). However, if a compounding ratio of an inorganic filler is increased in order to apply for a case of using a lead-free solder, a sufficient flowability cannot be obtained, which prevents the realization of this method.
In circumstances as described above, there is a demand for developing a resin composition for encapsulating a semiconductor device having a high flame resistance without addition of any flame retardant, and having a high solder reflow resistance which is applicable to a lead-free solder without declining flowability.